override关键字和new关键字之间的区别在于前者执行方法覆盖，后者执行方法隐藏。

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MSDN及其他

下面是一些代码来理解虚拟方法和非虚拟方法行为的区别:

class A
{
    public void foo()
    {
        Console.WriteLine("A::foo()");
    }
    public virtual void bar()
    {
        Console.WriteLine("A::bar()");
    }
}

class B : A
{
    public new void foo()
    {
        Console.WriteLine("B::foo()");
    }
    public override void bar()
    {
        Console.WriteLine("B::bar()");
    }
}

class Program
{
    static int Main(string[] args)
    {
        B b = new B();
        A a = b;
        a.foo(); // Prints A::foo
        b.foo(); // Prints B::foo
        a.bar(); // Prints B::bar
        b.bar(); // Prints B::bar
        return 0;
    }
}

Beyond just the technical details, I think using virtual/override communicates a lot of semantic information on the design. When you declare a method virtual, you indicate that you expect that implementing classes may want to provide their own, non-default implementations. Omitting this in a base class, likewise, declares the expectation that the default method ought to suffice for all implementing classes. Similarly, one can use abstract declarations to force implementing classes to provide their own implementation. Again, I think this communicates a lot about how the programmer expects the code to be used. If I were writing both the base and implementing classes and found myself using new I'd seriously rethink the decision not to make the method virtual in the parent and declare my intent specifically.

using System;  
using System.Text;  
  
namespace OverrideAndNew  
{  
    class Program  
    {  
        static void Main(string[] args)  
        {  
            BaseClass bc = new BaseClass();  
            DerivedClass dc = new DerivedClass();  
            BaseClass bcdc = new DerivedClass();  
  
            // The following two calls do what you would expect. They call  
            // the methods that are defined in BaseClass.  
            bc.Method1();  
            bc.Method2();  
            // Output:  
            // Base - Method1  
            // Base - Method2  
  
            // The following two calls do what you would expect. They call  
            // the methods that are defined in DerivedClass.  
            dc.Method1();  
            dc.Method2();  
            // Output:  
            // Derived - Method1  
            // Derived - Method2  
  
            // The following two calls produce different results, depending
            // on whether override (Method1) or new (Method2) is used.  
            bcdc.Method1();  
            bcdc.Method2();  
            // Output:  
            // Derived - Method1  
            // Base - Method2  
        }  
    }  
  
    class BaseClass  
    {  
        public virtual void Method1()  
        {  
            Console.WriteLine("Base - Method1");  
        }  
  
        public virtual void Method2()  
        {  
            Console.WriteLine("Base - Method2");  
        }  
    }  
  
    class DerivedClass : BaseClass  
    {  
        public override void Method1()  
        {  
            Console.WriteLine("Derived - Method1");  
        }  
  
        public new void Method2()  
        {  
            Console.WriteLine("Derived - Method2");  
        }  
    }  
}  

Virtual / override告诉编译器这两个方法是相关的，在某些情况下，当你认为你在调用第一个(虚拟)方法时，实际上应该调用第二个(被重写)方法。这是多态性的基础。

(new SubClass() as BaseClass).VirtualFoo()

将调用子类的重载VirtualFoo()方法。

New告诉编译器，您正在向派生类添加与基类中的方法同名的方法，但它们之间没有关系。

(new SubClass() as BaseClass).NewBar()

将调用BaseClass的NewBar()方法，而:

(new SubClass()).NewBar()

将调用子类的NewBar()方法。

不标记方法意味着:使用对象的编译类型绑定该方法，而不是运行时类型(静态绑定)。

用虚方法标记方法:使用对象的运行时类型绑定该方法，而不是编译时类型(动态绑定)。

在派生类中使用override标记基类虚方法意味着:这是使用对象的运行时类型绑定的方法(动态绑定)。

在派生类中用new标记基类虚方法意味着:这是一个新方法，它与基类中同名的方法没有关系，它应该使用对象的编译时类型进行绑定(静态绑定)。

在派生类中不标记基类虚方法意味着:该方法被标记为new(静态绑定)。

将一个方法标记为抽象意味着:这个方法是虚的，但是我不会为它声明一个主体，而且它的类也是抽象的(动态绑定)。